enable as_conversions lint

There were some very, uh, creative (and inconsistent) ways to convert
between numeric types in here...

src/database/abstraction/sqlite.rs

@@ -88,9 +88,14 @@ impl KeyValueDatabaseEngine for Arc<Engine> {
         // 1. convert MB to KiB
         // 2. divide by permanent connections + permanent iter connections + write connection
         // 3. round down to nearest integer
-        let cache_size_per_thread: u32 = ((config.db_cache_capacity_mb * 1024.0)
-            / ((num_cpus::get().max(1) * 2) + 1) as f64)
-            as u32;
+        #[allow(
+            clippy::as_conversions,
+            clippy::cast_possible_truncation,
+            clippy::cast_precision_loss,
+            clippy::cast_sign_loss
+        )]
+        let cache_size_per_thread = ((config.db_cache_capacity_mb * 1024.0)
+            / ((num_cpus::get() as f64 * 2.0) + 1.0)) as u32;
 
         let writer = Mutex::new(Engine::prepare_conn(&path, cache_size_per_thread)?);